Observations of Dislocation Sources in an Aluminium-Copper-Silicon Alloy

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Abstract
Electron microscopic evidence is presented which indicates that silicon particles in an Al-4% Cu alloy act as sources of glide dislocation loops during quenching. The Burgers vectors of the loops, identified by bright-field electron diffraction techniques, are of the type a/2. Small prismatic loops have been observed adjacent to the screw component of the glide loops in some instances. A semi-quantitative analysis of the forces near the particles is made. A critical particle size for dislocation nucleation is predicted. Some aspects of the equilibrium diameter of the glide loop are treated. The results of the calculations are compared with the electron microscopic observations, and some speculations about dispersion strengthened materials are made.